JBS 64(3) RGB.indd - Universidad Veracruzana

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The Secrets of Night-Blooming Bromeliads and Bats
Introduction
Pedro Adrián Aguilar-Rodríguez1,*, Thorsten Krömer1
and M. Cristina MacSwiney G.1
Unlike working with plant species that open their flowers during the day, studying
night-blooming bromeliads requires extensive field work under poor visibility conditions. The nocturnal (“night-shift”) pollinators, including bats and moths, are very
different in behavior and biology in comparison to their diurnal (“day-shift”) counterparts, such as hummingbirds and bees (i.e., different physiological needs, attraction
to different floral traits, duration of visits; Willmer 2011). Furthermore, the need for
special equipment to record nocturnal pollination may explain why night-blooming
bromeliads are less studied than the day-blooming species.
Among angiosperms, bromeliads are remarkable for their floral biology, since
most of the species appear to be primarily pollinated by vertebrates, rather than insects
(Krömer et al. 2006). Most other animal-pollinated plants, including the orchids, are
pollinated largely by insects. In the Neotropics, where almost all bromeliad species occur,
hummingbirds and bats are the most important vertebrate pollinators (Fleming et al.
2005). Hummingbirds are the most frequently reported bromeliad-pollinators (Kessler
& Krömer 2000; Carranza-Quiceno & Estévez-Varón 2008), resulting in a ratio of up
to 20 bird-pollinated (“ornithophilous”) to one bat-pollinated (“chiropterophilous”)
species (Sazima et al. 1999). Here, we present a brief overview of the knowledge about
bat-pollination in Bromeliaceae, with special focus on a recent study carried out by
our own working group.
Bat-Pollination Syndrome
In general, animal pollination syndromes are sets of floral characteristics that are
shared by unrelated plant species that are pollinated by a particular kind of animal. The
main groups of pollinators are bees, bumblebees, beetles, butterflies, hummingbirds,
and bats or other mammals (Willmer 2011). These floral characteristics include flower
morphology (size, shape, color, and marks in the perianth), floral rewards (nectar, pollen,
oils, resins, volatile compounds), and floral phenology. In particular, the bat-pollination
syndrome is a phenomenon generally restricted to the tropics and subtropics in the Old
and New World (Fleming et al. 2009). According to the literature, the most important
floral traits associated with bat-pollination are: 1) nocturnal or crepuscular anthesis (e.g.,
the flowers open at night or in the period of reduced light during the transition between
day and night); 2) pale or dullish colors in the petals (mostly white, pale green/yellow,
1Centro de Investigaciones Tropicales, Universidad Veracruzana, Casco de la ExHacienda Lucas
Martín, Privada de Araucarias S/N. Col. Periodistas, C.P. 91019, Xalapa, Veracruz, México.
*Corresponding author: [email protected]
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or creamy colors); 3) flagelliflory (flowers suspended on long stalks, away from the tree
branches); 4) cauliflory (flowers located directly on large branches or tree trunks); 5)
tubular or radially symmetrical flowers that act like a “mask” on the bat snout, but also
brush-type inflorescences with many smaller flowers that open near simultaneously;
6) musty, “onion”-like flower odors, sometimes with sulphur-compounds; 7) diluted
nectar (up to 17% of sugar); and 8) hexose-rich nectar (e.g., low sucrose content, but
high levels of glucose and fructose).
These floral traits probably evolved in most plant families as a modification to
an already existing pollination syndrome, such as the moth-pollination or even the
hummingbird-pollination syndrome (von Helversen 2003). Although some authors
have criticized this generalized concept, because most flowering plants appear to be
pollinated by more than one “type” of pollinator, it remains true that bat-pollinated
species share morphological characteristics in their flowers, which distinguish them
from other plants. In fact, the floral characteristics associated with bat-pollination have
evolved in at least 67 plant families around the world, including about 360 plant species
pollinated by the nectarivorous bat species that occur in the Neotropics, and belong
almost exclusively to the Phyllostomid family (Fleming et al. 2009).
Bat-Pollination And Bromeliads: Early Observations
Considering only floral traits, German biologist Fritz Müller (1897) noted that the
yellowish flowers of the Brazilian Vriesea jonghei (Libon ex K. Koch) E. Morren opened
at night, and emitted “an opossum-like scent,” producing copious nectar (Sazima et al.
1995). This anecdotal remark constitutes the first observation of a bromeliad species
with the putative bat-pollination syndrome. However, the first formal hypothesis on
bat-pollination among bromeliads came from Otto Porsch (1932), an Austrian biologist who suggested that bats might pollinate some species within the genera Vriesea,
Thecophyllum (whose species are now placed in the genera Guzmania and Werauhia) and
Alcantarea, based solely on the nocturnal anthesis and the dull colors of their flowers.
Several decades later, Stefan Vogel (1969) made the first confirmed report of batpollination in bromeliads from Brazil. Like his predecessors, he used the floral morphology to predict that at least 14 species of Vriesea (most of them now classified as members
of Werauhia) would be pollinated by bats. However, Vogel was also the first to conduct
mist-netting near flowering individuals of the endemic V. morrenii Wawra, capturing
two individuals of the glossophagine bat Anoura caudifer Geoffroy with bromeliad
pollen on their fur. In this way, Vogel initiated the path to more detailed studies that
shed light into one of the most overlooked plant-animal interactions.
After the publication of Vogel’s observations, the studies of bat-pollination in bromeliads during the 70´s and early 80´s were limited. The study of Salas (1973) realized
in Costa Rica on Vriesea ororiensis (Mez) L.B. Sm. & Pittendr. was the only contribution on bat-pollination in bromeliads for nearly a decade. However, the observation of
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chiropterophily seems doubtful and should be confirmed as the species has red bracts
and thus fits better within the hummingbird-pollination syndrome.
In the mid-1980’s, a couple of German scientists, Otto and Dagmar von Helversen,
both scholars in bioacoustics and bat ecology, made observations in another Brazilian
bromeliad, Vriesea bituminosa Wawra, that was visited by the same glossophagine bat
species observed earlier by Vogel (Dobat & Peikert-Holle 1985: 236). Considering
these observations, the von Helversen’s took living plants of Werauhia gladioliflora (H.
Wendl.) J.R. Grant and W. rugosa (Mez & Wercklé) J.R. Grant all the way to Germany,
where their floral nectar was used as food for the captive nectarivorous bat species Glossophaga soricina Pallas and Anoura geoffroyi Gray (Sazima et al. 1989).
Overview Of Current Knowledge
Since then, our knowledge about bat-pollination in bromeliads has continuously
grown. Bat-pollinated bromeliads have been studied in five countries: Brazil, Costa Rica,
Venezuela, Bolivia, and recently, Mexico. However, most of the studies were carried
out in Brazil, especially by the working group of Ivan and Marlies Sazima, and Silvana
Buzato. Furthermore, Otto von Helversen contributed to the ecological knowledge in
cooperation with Marco Tschapka.
Currently, it is presumed that, like in other plant families, bat-pollination in
bromeliads is a derivative pollination syndrome, evolved from the basal hummingbirdpollination syndrome (Benzing 2000; Kessler & Krömer 2000), and is reported mainly
from medium to high altitudes (i.e., Bolivian Andes region, ca. 1150-2400 m asl), but
evidence also exists for a lowland species (Werauhia gladioliflora in Costa Rica, 40-60
m.a.s.l.; Tschapka & von Helversen 2007).
Figure 1. Inflorescence of Guzmania calothyrsa Mez. Photo
by Thorsten Krömer.
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It is interesting to note that
many neotropical nectar-feeding
bats can be found in countries
with a high bromeliad diversity,
like Brazil and Bolivia, but most
of the documented examples of
bat-pollinators belong to only
one genus, the tail-less bats of
the genus Anoura, which are
common at medium to high
elevations (Koopman 1981).
We know that bat pollination in
bromeliads, at least in Bolivia,
is related to mid-elevations, and
common in humid montane
forests with high trees (Kessler
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& Krömer 2000), where bats of
this genus are abundant.
As mentioned above, the
greatest number of documented
cases of bat-pollination can
be found within Vriesea and
Werauhia (Grant 1995). In
fact, Werauhia, including about
93 species of which 80 occur
in Costa Rica and Panama
(Krömer et al. 2007), could
Figure 2. Inflorescence of Puya ferruginea (Ruiz & Pav.) L.B.
be entirely bat-pollinated, and
Sm. Photo by Thorsten Krömer.
thus, demonstrate the importance of bats as pollinators and selective agents in the evolution of bromeliads. In earlier
studies, these species now placed in Werauhia were usually treated as belonging to Vriesea.
Up to now, bat-pollination in Bromeliaceae is reported or suggested in seven
genera and 24 species, within
the 58 genera and about 3352
reported bromeliad species (Luther 2012). Thus, only about
0.8% of all bromeliad species
have been proposed to be batpollinated, with current reports in Encholirium (E. glaziovii, E. vogelii), Guzmania (G.
calothyrsa[Fig. 1], G. danielii, G.
killipiana, G. morreniana, G. retusa, G. sphaeroidea), Pitcairnia
(P. brongniartiana, P. trianae),
Puya (P. ferruginea [Fig. 2]),
Tillandsia (T. heterophylla, T.
macropetala; Fig. 5 and 6), Vriesea (V. bituminosa, V. gigantea, V. Figure 3. Flowers of Werauhia noctiflorens T. Krömer,
longicaulis, V. longiscapa, V. mor- Espejo, López-Ferr. & Acebey. Photo by Thorsten Krömer.
renii, V. platynema, V. sazimae),
and Werauhia (W. gladioliflora, W. kupperiana, W. ororiensis, W. rugosa; Fig. 3) (Krömer
2003; Fleming et al. 2009; Krömer et al. 2012; Christianini et al. 2013; Aguilar-Rodríguez
et al. 2014; in press). Nevertheless, all of the more than 90 species of Werauhia share
characteristics that suggest they might be chiropterophilous, in addition to one species
of Billbergia (Krömer et al. 2006, Krömer et al. 2008). In this manner, chiropterophily
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Figure 4. A. Billbergia robert-readii E. Gross & Rauh in habitat B. Inflorescence of
Billbergia robert-readii. Photos by Thorsten Krömer.
bats, it would constitute the first report within Bromelioideae.
has been confirmed in two
out of eight
subfamilies
of the bromeliads, although most
frequently
in Tillandsioideae. If
Billbergia
robert-readii
E. Gross &
Rauh (Fig.
4) is indeed
pollinated by
Most of the bat-pollinated bromeliads studied have zygomorphic bisexual flowers. In
addition, excluding some Vriesea species with reddish petals (Sazima et al. 1995), most of
them have pale green, yellow, or whitish
petals and, in most cases, the floral bracts
form a “dish” that helps to accumulate
the relatively large quantities of nectar
produced by their flowers. The flowering pattern is similar among species of
different genera, being most common to
open only one or two flowers per night,
during a long period. Furthermore,
nectar traits, mainly sugar composition
and concentration are within the range
of those present in bat-pollinated species
in other families, offering diluted nectar
and with more glucose and fructose over
sucrose (Krömer et al. 2008).
Figure 5. Tillandsia macropetala in habitat. Photo
by Thorsten Krömer.
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Also, most bat-pollinated bromeliads
are epiphytes, and thus may be more
accessible to a nectarivorous bat with
hovering flight. However, Encholirium
species are exceptional among chiropterophilous bromeliads, because they
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Bromeliads and Bats
are mainly terrestrial, and
with a racemose or brushlike inflorescence bearing
many open flowers each
night, in contrast to the
spike-like inflorescences
and epiphytic habit of
most other bat-pollinated
bromeliads.
Figure 6. A. Flower of Tillandsia heterophylla E. Morren. B. Flower
of Tillandsia macropetala Wawra. Photos by Pedro Aguilar.
The best-documented
case of bat-pollination
among bromeliads how-
ever comes from Costa
Rica and the species
Werauhia gladioliflora. Contrary to other
works, this bromeliad
has been studied in
tropical lowland rainforest of La Selva biological station, where
it receives visits by at
least four different bat
species. It is known
that this bromeliad is
important to the local nectarivorous bats, Figure 8. The nectarivorous bat Anoura geoffroyi pollinating a flower
providing a valuable of Tillandsia macropetala. Photo by Pedro Aguilar.
resource in the form of
nectar and pollen almost all year around (Tschapka & von Helversen 2007).
A Case Study: Bat-Pollination In Mexican Tillandsias
In this final section we will present our ongoing work on a rare case of bat-pollination in Tillandsia, the most species-rich genus within the Bromeliaceae. Tillandsia
comprises about a third of all bromeliads, and most studies report hummingbirds as
the main pollinators. However, members of the subgenus Pseudoalcantarea have been
proposed to be pollinated by nocturnal animals, because of their night-blooming flowers (Benzing 2000).
In a comprehensive study of nectar traits among bromeliads (Krömer et al. 2008),
two Mexican species, Tillandsia macropetala Wawra (Fig. 6 and 7); which was reJ. Bromeliad Soc. 64(3). 2014.
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Figure 9. Anoura geoffroyi Gray, the bat-pollinator of Tillandsia macropetala and T.
heterophylla in Veracruz, Mexico. Photo by Pedro Aguilar.
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cently recognized as a species distinct from T. viridiflora (Beer) Baker (Krömer et al.
2012) and T. heterophylla E. Morren (Fig. 3), showed sugar constituents and concentration similar to other bat-pollinated bromeliads, in addition to pale green or white petals
and crepuscular blooming. This suggested a probability that those species could be, in
fact, bat-pollinated, unlike any other Tillandsia species studied before (Gardner 1986).
This hypothesis remained untested until the Master thesis of the first author
confirmed that in the endangered humid montane forests of central Veracruz, both
species are pollinated by the tail-less nectarivorous bat, Anoura geoffroyi (Fig. 8 and
9). This was supported by nocturnal camera recordings, direct captures of bats near
inflorescences with fresh flowers, and the presence of bromeliad pollen on the fur of
the captured bats (Aguilar-Rodríguez et al. 2014). It is worth noting that in the case of
T. macropetala, its flowers do not fit the conventional bat-pollination syndrome (Fig.
6B): it has a faint sweet odor (without the sweat/onion-like scent present in Werauhia),
and an actinomorphic helicoiform corolla, with band-like petals (unlike members of
Vriesea and Werauhia). Whereas A. geoffroyi was the only pollinator recorded for T.
macropetala, the study of T. heterophylla interestingly also revealed diurnal pollinators,
such as hummingbirds and bees, as its flowers remain open until the next afternoon
and their visits produce fruits (Aguilar-Rodríguez et al. in press).
This brief overview shows that most of the information on bat-pollination in bromeliads is relatively recent, and still scarce. We hope to continue our work in Mexico, in
other locations and with different species of Tillandsia, in order to determine the entire
range of this previously undescribed interaction. Documenting these plant-pollinator
interactions may provide information necessary for the implementation of conservation strategies, and thus we hope to help to secure the survival of both, bromeliads
and their bat-pollinators.
Acknowledgements
We thank Pedro Díaz-Jiménez, Valeria Guzmán-Jacob, and Bruce Holst for
their comments on the manuscript. We also thank to Andréa Araujo, Marília Barros,
Jeanett Escobedo, and Marlies Sazima for their contributions during the research for
the manuscript. The M.Sc. study by the senior author was supported by the Mexican
Council on Science and Technology (CONACYT grant number 59406) and the camera
equipment used by Thorsten Krömer was generously funded by The Bromeliad Society
International.
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